Quoting Nigel Thornberry:" Please don't try castor oil, it poses risks to both you and the baby and it's not even guarenteed to ... [snip!] ... it could cause baby to pass meconium which could be fatal. The best thing you can do is walk, have sex, and just wait it out. "
That usually works, but if she really has severe pre-e like she says then she doesn't need to be doing anything, especially walking or sex. She should be on really strict bedrest. And if it is in fact severe, then the doctor should probably already be thinking about inducing her. When it gets to the point of being severe, that's usually what they do. They'll wait it out as long as possible id it's mild but I was induced the same day they realized mine was severe.